Wireless and like receiver



Nov. 29, w38. J, ROBWSON 2,138,746

WIRELESS AND LIKE RECEIVER Filed Sept. l, 1,954

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aff-irre@ Patented Nov. 29, 1938 WIRELESS AND LIKE RECEIVER JamesRobinson, London, England.

Application september 1, 1934, serial No. 742,487 In Great BritainSeptember 9, 1933 4 Claims.

This invention relates to wireless and like receivers for modulated, e,g. interrupted, carrierwave signals, and o-ne object of the invention isto determine the relationship between the amplitude 5 of thecarrier-wave and the amplitude of the sideband frequencies used in thereceiver for reproduction of the signals.

In one Well-known form of receiving apparatus there is provided aselective system providing a response which is substantially uniformover a band of frequencies which includes the carrier frequency and alsothe essential side bands of the transmission and providing a lowresponse outside this band in order to minimize interference. Such areceiver is usually referred to as one with band-pass selectivity.

In another form of receiver there is employed a resonator of low dampingor high selectivity tuned to the carrier frequency of the signals to bereceived and providing a high response at this frequency as comparedwith the response at adjacent frequencies including the essentialside-band frequencies. In this case additional benefits are obtained asregards overall selectivity by reason of the comparatively high value ofthe received carrier frequency, although it is necessary to correct thedistortion that is obtained of the modulation signals as a result of thehigh selectivity. Certain different technique is required for thislatter type of receiver, for instance, in some cases to provide rathermore amplification than with other forms of receivers owing to the smallamplitude at which the side band frequencies are received as comparedwith the amplitude of the response of the carrier frequency.

Another object of the present invention is to provide a receiver inwhich the advantages' of both the forms of receiver mentioned above areobtained. That is to say, it is an object of this 40 invention toprovide a receiver by means of which the side-bands are received at suchvolume that a normal amount of amplification is sufficient for ordinarypurposes and at the same time a comparatively large response for thecarrier frequency is obtained in order to secure the advantages in theeifective selectivity of the apparatus.

The present invention comprises a wireless or like receiver formodulated carrier-wave-transmissions in which there is providedsignal-selective means comprising the combination of a resonant deviceof low damping, such as a piezoelectric crystal tuned to the frequencyof the carrierwave of the signals to be received (or frequencyconversions thereof), a comparatively broadlytuned resonant device forreceiving at least one (Cl. Z50-20) side-band of the signals atVsubstantially uniform amplitude, means for applying the incomingsignals to both of these resonant devices, and a rectier for the signalsto which the combined output of the two resonators is applied. Theresonant device of low damping provides a response of Very largeamplitude for the carrier frequency as compared with the response forthe side-band frequencies. II'he broadly-tuned resonant device, on theother hand, provides a larger response for the frequencies of at leastone side-band. VThus, by the combination of the outputs of these tworesonant devices, any interference is reduced in intensity due to thehigh amplitude of the carrier frequency and also the wanted modulationfrequencies may be reproduced without a high degree of low frequencyamplification being necessary. By a reso-nant device of low damping ismeant one having less than normal damping in wireless receivers andincluding Zero or even negative damping.

In one form of the invention the signal output of the resonant device oflow damping is provided by a portion of the output of the broadly-tunedresonant device. In another form the incoming signals are fed separatelyto both of the resonant devices which thus constitute parallel paths forthe signals in the receiver.

According to a feature of the invention, means is provided'for adjustingthe relative phase and/ or amplitude of the signals which are combinedfrom the outputs of the two resonant devices. In this manner properphase relation of the two outputs may be ensured.

In the receiver according to this invention the side-band frequencies ofthe signals are received mainly by the broadly-tuned resonant device andthe carrier-wave component is to a large extent isolated and separatelyreceived by the resonant device of low damping. By rotating the phase ofthe carrier with respect to both side-bands, a variation in the totaloutput may be obtained. Also, in cases where only one side-band isreceived, the carrier component received by the resonant device of lowdamping may be more or less opposed to the carrier component received bythe broadly-tuned lresonant device to control the total volume of theoutput signals. Thus, by adjusting the phase relation of output of theresonant device of low damping with respect to the output of thebroadly-tuned resonant device, a control of the total output of thereceiver is obtained and a further feature of this invention consists inproviding means to control this phase relationship automaticallyaccording to the strength of the received signals. Furthermore,additional means, such as a limiting device, may be provided forobtaining a more thorough isolation of the carrier component.

Several specific forms of wireless receiver according to the inventionare shown by way of examples in the accompanying drawing, in which:-

Figure 1 is a diagrammatical representation of one form of receiver inwhich the resonant device of low damping is connected to the output ofthe other resonant device. Y

Figure 2 is a similar View of another form of receiver in which theresonant devices are separately fed by the incoming signals.

Figures 3 and 4 show resonance curves of typical forms of the receiversshown in Figures 1 and 2, and

Figure 5 diagrammatically represents a further form of receiver withadditional means for isolating the'carrier component of the signals;

Referring to Figure 1 of the drawing, there is shown diagrammatically areceiver of the superheterodyne type comprising an initial amplier I5for the incoming signals, an oscillator and detector II for convertingthe signals to a. constant intermediate frequency and an amplifier i2for the intermediate frequency signals. The intermediate frequencyamplifier I2 comprises a circuit I3, comprising an inductance I4 and acapacity I5, broadly tuned to the intermediate frcquency of the signals.This broadly-tuned circuit I3 is coupled through an impedance I6 to adetector II which is in turn coupled to an output amplifier I8 for themodulation frequency output. Connected in parallel with the impedance I6there is provided a piezo-electric device I9 which is in tune with thetuned circuit I3. The impedance I6 may comprise a resistance or acondenser or an inductance and in the latter case it `may form, with theresidual capacity of the piezo-electric device I9, a tuned circuit whichmay appropriately be used for rejecting a specie frequency other thanthat of the converted carrier frequency of the signals.

In this receiver the broadly-tuned circuit I3 provides a substantiallyuniform response for the band of frequencies tobe received. Thepiezoelectric crystal I9 provides a response for the convertedcarrier-wave of the signal output from the tuned circuit I3 which mustbe made considerably greater than the response at other frequencies, forinstance, by means of independent amplication or different couplings.The combined response of the tuned circuit I3 and the piezo-electriccrystal I9 as applied to the detector Il is thus constituted by-asubstantially uniform response for the side-band frequencies of thesignals together with a considerably greater response for the convertedcarrier frequency of the signals. Phase-adjusting means, for instance asindicated at 29, may be provided to ensure the appropriate phaserelationship between the output of the piezo-electric device I9 and thatof the tuned circuit I3 as combined at the detector I 1.

In Figure 3 there is shown at 50 the resonance curve of thepiezo-electric device I9 tuned to a frequency f corresponding to thecarrier-wave of the intermediate frequency signals. At 5I there isindicated the resonance curve of the broadlytuned circuit I3 and at 52there is shown theresultant resonance curve of the system showing thelarge response for side-band frequencies together with the .greaterresponse at the intermediate carrier frequency whereby the knownbeneficial eifects for minimizing interference are obtained at thedetector I1 of the receiver.

In Figure 2 of the drawing there is also shown a receiver of thesuper-heterodyne type comprising an initial amplifier I0, an oscillatorand detector I I and an intermediate frequency amplier I2. Thisintermediate frequency amplier comprises a broadly-tuned circuit I3feeding a detector Il through an amplier 20 and if desired a phase andamplitude-adjusting device 2I of known form comprising, for instance, acircuit containing variable inductance, capacity and resistance.Connected in parallel with the devices I 3, 20 and 2! there are provideda piezo-electric crystal I9 also feeding the detector I1 through anamplier 22 and a phase and amplitude ad- `iusting device 23. In thisform of receiver the piezo-electric crystal is tuned to the converted orintermediate carrier frequency of the signals and provides an outputapplied to the detector I'I which is considerably greater at theresonant frequency than at other frequencies. The broadly-tuned resonantdevice I3 provides a large response for the side-band frequencies whichis applied to the detector I'I and combined with the output of thepiezo-electric crystal I9.

In the arrangement indicated in Figure 2 the broadly-tuned resonantdevice I3 may be tuned to the intermediate carrier frequency of thesignals as described with reference to Figure 1 in which case the totalresponse is of the form indicated in Figure 3. Alternatively, thisbroadlytuned resonant device I3 may be tuned to a frequency displacedfrom the intermediate carrier frequency, for instance by an amount equalto the highest wanted modulation frequency, for instance, 5000 to 6000cycles per second for telephony so that this resonant device isresponsive mainly to one side-band of the signals. Thus, as shown inFigure 4, the curve 53 represents the response of the piezo-electricdevice I9, the curve 5d the response of the broadly-tuned circuit I3 andthe curve 55 indicates the resultant correspending to the total signalsfed to the detector VIl'. It will be understood that the resultantcurves shown in Figures 3 and 4 are qualitative only to indicategenerally the form of the response of receivers according to theinvention and that the actual quantitative form will depend upon thephase relationship of the combned signals in each particular case.

In the form of receiver indicated in Figure 2 it is preferable toprovide means to change the tuning of the circuit I3 for one or theother side bands of the signals for the purpose of minimizinginterference. Thus, the resonant circuit IS may normally be tuned forthe lower sideband and a condenser 24 in series with a switch 25 may beprovided in parallel with the circuit I3 for changing the tuning to theother sideband.

It will be understood that the broadly-tuned circuit I3 may be of anyform, either a simple circuit as shown or a complex circuit such as aband-pass circuit, the width of the band being such as to include bothor only one of the sidebands of the signals. Alternatively, separatetuned circuits may be employed with a switch to introduce either one foroperation. When lemploying a tuned system of the band-pass type for asingle side-band, the band-pass range of frequencies may include thefrequency of the intermediate carrier-wave or alternatively thisfrequency may be outside the range of the bandpass system, especially incircumstances where the modulation of the signals to be received is inthe super-sonic range.

By the use of a broadly-tuned resonant device, tuned to a frequencyother than the carrier frequency of the signals, the response to themodulation frequencies may be non-uniform and, if desired, means may beprovided, for example in the low frequency part of the receiver, forcorrecting the distortion thus produced.

Referring again to Figure 2 of the drawing, the amplifiers 2i! and 22are provided for separately amplifying the signals passed through thepiezo-electric device I9 and the broadly-tuned circuit i3. It ispreferable to amplify the output of the piezo-electric device by ahigher factor than the amplification of the response of thebroadly-tuned circuit I3 in order to provide a maximum amplitude for theformer which is considerably greater than that of the broadlytunedcircuit, for example ten times greater.

Referring again to Figure 2 of the drawing, the volume output of thereceiver may be controlled by relative adjustment of thephasecontrolling devices 2l and 23 since by rotating the phase of thecarrier-wave as obtained from the piezo-electric device I9 with respectto the side-bands which are received mainly by the broadly-tunedresonant device i3, a variation in resulting modulation signal strengthis obtained. rIhis control by phase variation may be effectedautomatically by means such as a variable condenser 26 forming part ofthe phase-controlling means 23 and operated automatically by anelectro-magnetic device 2l' controlled by a portion of the signal outputderived for instance from the amplifier 22 for the output of thepiezoelectric crystal.

Alternatively, a portion of the output of the piezo-electric crystal I9or preferably the output of the following amplifier 22 may be utilizedfor controlling automatically in the well-known manner the amplificationof the receiver according to the volume output by providing a biasingpotential for one or more amplifying valves of the receiver.

.The output of the piezo-electric crystal or the amplier 22 may also beutilized in the known manner to suppress the output of the receiver whenno carrier-wave signals are being received or when off tune, for exampleby providing, by means of a rectifier 2%, a bias for suppressingoperation of a valve or valves of the output amplifier I8 andconsequently the output of the receiver when the signals are receivedare below a minimum value.

It is preferable in cases where the output of the piezo-electric crystalis to be varied as regards phase with respect to the output of thebroadly-tuned resonant device for the purpose of volume control to havethe output of the piezoelectric device as free as possible of modulationsignal components and in such circumstances additional devices may beemployed for this purpose.

In Figure 5 there is shown a receiver comprising a high-frequencyamplifier 30, a detector 3i and an output amplier 32. In this case aportion of the input signal energy is applied to an oscillating detector33 to convert the signals to an intermediate frequency which is constantfor a range of incoming signals. The output from this oscillatingdetector is applied to a piezo-electric device 34 tuned to theintermediate frequency and by reason of the low damping of thispiezo-electric device the output therefrom comprises a carrier componentwhich is at a high value compared with the modulation components of thesignals. This carrier component is further isolated by means of alimiting device 35 followed by a filter 36 tuned to the intermediatefrequency. This isolated carrier of intermediate frequency is fed backto the detector-oscillator which is'provided with an output circuit 31tuned to the original carrier frequency from which there is obtained thecarrier component of the original frequency. The carrier component ofthe signals thus isolated is fed through phase and amplitude adjustingmeans 38 to a highfrequency circuit of the normal receiver and providesan effect of increased selectivity, as hereinbefore described.Alternatively, the isolated carrier at low frequency may be combinedwith a portion of separately, the resulting output at the originalcarrier frequency being fed to the receiving circuit.

The phase and amplitude controlling means indicated at 38 is preferablyprovided for controlling the volume output of the receiver for exampleautomatically according to the input signals as hereinbefore describedwith reference to Figure 2.

Modification may be made in the specific forms of receiver hereinbeforedescribed. For instance, the outputs of the resonant device of lowdamping and the broadly-tuned resonant device may be combined either inthe assisting sense or in the opposed sense. Further, the impedance I6in Figure l may be constituted by the electrode capacity of thepiezo-electric device and in this case any phase adjustment if necessarymay be effected by slightly detuning the piezo-electric device.

I claim:-

1. In a Wireless or like receiver for modulated carrier-wave signals,signal-selective means comprising the combination of a broadly-tunedresonant device for receiving at least one side-band of the signals atsubstantially uniform amplitude, means for applying the signals to saidbroadlytuned resonant device, means for converting the frequency of thesignals to a frequency that is constant for a range of differentsignals, a resonant device of low damping tuned to the converte-dfrequency of the signals, means for applying the converted signals tosaid resonant device of low damping, means for reconverting the outputof said resonant device of low damping to the original signal frequency,means for combining said converted output with the output of thebroadly-tuned resonant device, a rectifier for the signals and means forapplying the combined output to the said rectifier.

2. In a Wireless or like receiver for modulated. carrier-Wavetransmission, signal-selective means comprising the combination o-f abroadly-tuned resonant device for receiving at least one sideband of thesignals at substantially uniform amplitude, means for applying theincoming signals to said broadly-tuned resonant device, means forconverting the frequency of the incoming signals to a frequency which isconstant for a range of received signals, a piezo-electric device tunedto said frequency, means for applying said converted signals to saidpiezo-electric device, limiting means for further isolating thecarrier-wave output of the piezo-electric device, means for reconvertingthe output of said limiting device the oscillator output, and rectifiedto the original signal frequency, means for combining said convertedoutput to the output of the broadly-tuned resonant device, a rectifierfor the signals and means for applying the combined output of theresonant devices to the said rectifier.

3. In a wireless or like receiver for modulated carrier-Wave signals,signal-selective means comprising the combination of a broadly-tunedresonant Idevice for receiving at least one side-band of the signals atsubstantially uniform amplitude, means for applying the signals to saidbroadlytuned resonant device, means for yconverting the frequency of thesignalsv to a frequency that is constant for a range of differentsignals, a resonant device of low damping tuned to the converted signalfrequency, means for applying the converted signals to said resonantdevice of low damping, means for reconverting theoutput of said resonantdevice of low damping to the original signal frequency, means foradjusting the relative phase of the converted output of the resonantdevice of low damping and the output of the broadly-tuned resonantdevice, means for combining said converted output with the output of thebroadly-tuned resonant device, a rectier for the signals and means forapplying the combine-d output to the said rectifier.

- 4. In a Wireless or like receiver for modulated carrier-Wavetransmission, signal-selective means comprising the combination of abroadly-tuned resonant device for receiving at least one side-- band ofthe signals at substantially uniform amplitude, means for applying theincoming signals to said broadly-tuned resonant device, means forconverting the frequency of the incoming signals to a frequency which isconstant for a range of received signals, a piezo-electric device tunedto said frequency, means for applying said converted signals to saidpiezo-electric device, limiting means for further isolating thecarrierwave output of the piezo-electric device, means for reconvertingthe output of said limiting device to the original signal frequency,means for adjusting the relative phase of the reconverted output and theoutput of the broadly tuned resonant device, means for combining saidreconverted output with the output of the broadlytuned resonant device,a rectifier for the signals and means for applying the combined outputof the resonant devices to the said rectifier.

JAMES ROBINSON.

